Good Sci-Fi books, anyone?

That's a lot of pages. It's hard to satisfy that with a single book, you'll probably have to go with a whole series.

The first one you can try is Atlas Shrugged. It IS a single book, one of the longest english-language novels ever written, although it is divided into three parts. Accordingly, reading it is something of an undertaking (in particular, it features a monologue by one of the characters that extends to something like- I am not kidding- 56 pages in length). It's not really a sci-fi story, but it is speculative fiction, more along the lines of dieselpunk; there are no nukes or computers, but there are a number of other strange technologies that never existed in the real world. Basically the whole story is a giant platform for the author (Ayn Rand) to drill her philosophical and economic opinions into your head, so be warned.

Other than that, well, you can try the Ringworld series (it has four books), the Foundation series (originally three books, but more were written later on), or the series by Vernor Vinge consisting of A Deepness in the Sky and A Fire upon the Deep (note that the latter book was written first, but takes place second in chronological order). Both are decent science fiction, with Foundation and Ringworld in particular being some of the most prominent works in the field. Note that the universes of Ringworld and Foundation both feature other stories that take place in them but are not actually part of the same series.

The Windup Girl by Paolo Baciqalupi

Ender Wiggins series by Orson Scott Card

Dune series by Frank Herbert

Foundation series by Isaac Asimov

Stranger in a Strange Land by Robert Heinlein

Red Mars by Kim Stanley Robinson

You can read a series instead of one big mammoth book.

The Ender Series by Orson Scott Card

It begins with Ender's Game and then there's the series about Ender.

There is also a compantion series that begins with Ender's Shadow which is Ender's Game from a different character's perspective and then goes off into its own series.

That should keep you thinking for a while. Those books are absolutely brilliant and most if not all libraries have them.